The present invention relates to a control valve for variable displacement compressors that are used in vehicle air conditioners.
A typical variable displacement compressor includes a control passage for connecting a discharge pressure zone with a crank chamber. The pressure in the crank chamber is adjusted to change the inclination of a cam plate. Accordingly, the displacement is controlled.
Japanese Unexamined Patent Publication No. 4-119271 discloses a typical control valve for variable displacement compressors. As shown in FIG. 7, this control valve has a valve chamber 101 in a distal portion of a valve housing 102. The valve chamber 101 is connected to a discharge pressure zone by the upstream portion of a control passage 103. The valve chamber 101 is also connected to a crank chamber by a valve hole 104, a port 105 and the downstream portion of the control passage 103. The valve hole 104 is formed axially in the housing 102 and the port 105 is perpendicular to the valve hole 104. A valve body 106 is housed in the valve chamber 101 to open and close the valve hole 104.
A pressure sensing chamber 107 is formed adjacent to the valve chamber 101 and is connected to a suction pressure zone. A bellows 108 is housed in the pressure sensing chamber 107 to detect the pressure of the suction pressure zone. The pressure sensing chamber 107 is separated from the valve chamber 101 by a dividing wall 102a. A guide hole 109 is formed in the dividing wall 102a to be continuous with the valve hole 104. The chambers 101 and 107 are therefore connected to each other. A rod 110 is slidably fitted in the guide hole 109 to couple the bellows 108 with the valve body 106. The bellows 108 is deformed in accordance with the suction pressure of the refrigerant gas. The deformation of the bellows 108 is transmitted to the valve body 106 by the rod 110.
A solenoid portion 111 is attached to a proximal portion of the valve housing 102 and is coupled to the valve body 106 by the bellows 108. The solenoid portion 111 is excited and de-excited for changing the attraction force between a fixed iron core 112 and a movable iron core 113. Accordingly, the load acting on the valve body 106 is changed. Therefore, the opening size of the control passage 103 is determined by the equilibrium of forces, such as the force of the solenoid portion 111 and the force of the bellows 108.
The pressure in the port 105 is relatively high and the pressure in the pressure sensing chamber 107 is relatively low. The rod 110 and the guide hole 109 are machined with meticulous care for allowing the rod 110 to slide in the hole 109 and for preventing leakage of gas between the port 105 and the pressure sensing chamber 107. However, small machining errors are inevitable, and the space between the surface of the rod 110 and the surface of the guide hole 109 is different between a location near the port 105 and a location near the pressure sensing chamber 107. Particularly, when the space near the port 105 is smaller than the space near the pressure sensing chamber 107, the pressure difference between the port 105 and the pressure sensing chamber 107 generates a lateral force acting on the rod 110. The lateral force presses the rod 110 against the surface of the guide hole 109, which increases the sliding resistance between the rod 110 and the guide hole 109 (this phenomena will hereafter be referred to as fluid fixation).
A recent trend is to reduce the size of the solenoid portion 111 to reduce the size of the compressor. In a valve having a small solenoid portion 111, the bellows 108 is relatively small and the valve body 106 is moved by the equilibrium of the difference between small forces, that is, the force of the solenoid portion 111 and the force of the bellows 108. Therefore, the control valve is easily affected by an increase of the sliding resistance between the rod 110 and the guide hole 109 due to the fluid fixation. As a result, even a small sliding resistance, which would be negligible if the bellows 108 were large, causes hysteresis. Therefore, the controllability of the displacement significantly deteriorates.
The present invention was made in view of drawbacks in the above described prior art. Accordingly, it is an objective of the present invention to provide a control valve for a variable displacement compressor that reduces sliding resistance between a rod and a guide hole.
To achieve the foregoing objective, the present invention provides a control valve for a variable displacement compressor. The control valve includes a valve body. The valve body opens and closes a control passage, which connects a control pressure chamber with a suction pressure zone or with a discharge pressure zone, to adjust the opening size of the control passage for varying the displacement of the compressor. The valve body is opened and closed by a drive member. A dividing wall separates a portion that accommodates the valve body from a portion that accommodates the drive member. A guide hole is formed in the dividing wall to communicate the valve body accommodating portion with the drive member accommodating portion. A sliding rod is located in the guide hole to operably couple the valve body to the drive member. The control valve is characterized by means for preventing fluid fixation. The fluid fixation preventing means is located on at least one of the outer surface of the rod and on the inner surface of the guide hole.
The invention of the above structure has the means for preventing fluid fixation between the rod and the guide hole, which decreases the hysteresis of the control valve and prevents deterioration of the displacement controlling performance of the control valve.
In the above structure, the means may include a tapered surface formed on at least one of the outer surface of the rod and the inner surface of the guide hole such that the space between the outer surface of the rod and the inner surface of the guide hole widens toward one of the valve body accommodating portion and the drive member accommodating portion that has a higher pressure.
If the axis of the rod is displaced from the axis of the guide hole for some reason, the rod receives a lateral force, the direction of which is opposite to the displacement direction. The misalignment of the axes is automatically corrected.
In the above structures, the tapered surface may be one of a plurality of tapered surfaces formed along the axial direction of the rod.
In this structure, the cross-sectional area of the space between the outer surface of the rod and the inner surface of the guide hole changes in the axial direction in a completed fashion and functions like a labyrinth seal. This effectively prevents pressure leakage and refrigerant gas leakage between the high pressure location and the low pressure location.
In the above structure, the outer surface of the rod may be tapered such that the diameter of the rod decreases toward one of the valve body accommodating portion and the drive member accommodating portion that has higher pressure. This eliminates the necessity for tapering the inner wall of the guide hole, which is formed in the dividing wall and has a small cross-section, by inserting a tool into the guide hole.
In the above structures, the means may include a circumferential annular groove formed in at least one of the outer surface of the rod and the inner surface of the guide hole.
The annular groove circumferentially equalizes the pressure in the space between the outer surface of the rod and the inner surface of the guide hole. Accordingly, fluid fixation does not occur between the rod and the guide hole.
If the annular groove is formed in the outer surface of the rod, the groove is easily formed.
In the above structure, the drive member may include a pressure sensing mechanism having a pressure sensing chamber and a pressure sensing member located in the pressure sensing chamber. The pressure sensing chamber is connected either with the suction pressure zone or with the control pressure chamber by a pressure introduction passage. The rod operably couples the pressure sensing member with the valve body.
In this structure, the pressure sensing member is deformed by pressure in the pressure sensing chamber, that is, by either the pressure of the suction pressure zone or the pressure in the control pressure chamber. The deformation is transmitted to the valve body by the rod.
In the above structure, the drive member may include a solenoid portion. The solenoid portion is excited and de-excited to actuate a plunger accommodated in a plunger chamber. The rod operably couples the plunger with the valve body.
In this structure, the plunger is moved by excitation and de-excitation of the solenoid portion. The movement of the plunger is transmitted to the valve body by the rod.
In the above structure, the drive member may include a pressure sensing mechanism and a solenoid portion. The pressure sensing mechanism may include a pressure sensing chamber and a pressure sensing member located in the pressure sensing chamber. The pressure sensing chamber is connected either with the suction pressure zone or with the control pressure chamber by a pressure introduction passage. The solenoid portion is excited and de-excited to actuate a plunger accommodated in a plunger chamber. The rod may include a first rod portion, which operably couples the pressure sensing member with the valve body, and a second rod portion, which operably couples the plunger with the valve body.
In this structure, the opening size of the control passage is determined by the position of the valve body, which is determined by the equilibrium of the force of the pressure sensing mechanism and the force of the solenoid portion.
In the above structure, the control passage may connect the discharge pressure zone with the control pressure chamber.
In this structure, the amount of refrigerant gas drawn into the control pressure chamber is adjusted for controlling the displacement. Highly pressurized gas is introduced into the control valve. Fluid fixation between the rod and the guide hole causes the rod to be pressed against the guide hole by a greater force compared to a control valve that adjusts the amount of refrigerant gas discharged from the control pressure chamber to control the compressor displacement. Therefore, the present invention has a great advantage.